Inertial navigation of a platform is based upon the integration of specific forces and angular rates measured by inertial sensors (e.g. accelerometer, gyroscopes) by a device containing the sensors. In general, the device is positioned within the platform and commonly strapped to the platform, and measurements from the device may be used to determine the position, velocity and attitude of the device and/or the platform.
The platform may be a motion-capable platform that may be temporarily stationary (e.g. a person, a vehicle or a vessel of any type. The vessel may be land-based, marine or airborne.
Alignment of the inertial sensors within the platform (and with the platform's forward, transversal and vertical axis) is critical for inertial navigation. If the inertial sensors, such as accelerometers and gyroscopes are not exactly aligned with the platform, the positions and attitude calculated using the readings of the inertial sensors will not be representative of the platform. Fixing the inertial sensors within the platform is thus a requirement for navigation systems that provide high accuracy navigation solutions.
For strapped systems, one known means for ensuring optimal navigation solutions is to utilize careful manual mounting of the inertial sensors within the platform. However, portable navigation devices (or navigation-capable devices) are able to move whether constrained or unconstrained within the platform (such as for example a person or vehicle), so careful mounting is not an option.
For navigation, mobile/smart phones are becoming very popular as they come equipped with Assisted Global Positioning System (AGPS) chipsets (in addition to significantly improving the startup performance by utilizing network connection) also further use high sensitivity capabilities to provide absolute positions of the platform (e.g. user) even in some environments that cannot guarantee clear line of sight to satellite signals. Deep indoor or challenging outdoor navigation or localization incorporates cell tower ID or, if possible, cell towers trilateration for a position fix where AGPS solution is unavailable. Despite these two positioning methods that already come in many mobile devices, accurate indoor localization still presents a challenge and fails to satisfy the accuracy demands of today's location based services (LBS). Additionally, these methods may only provide the absolute heading of the platform without any information on the device's heading.
Many mobile devices, such as mobile phones, are equipped with Micro Electro Mechanical System (MEMS) sensors that are used predominantly for screen control and entertainment applications. These sensors have not been broadly used to date for navigation purposes due to very high noise, large random drift rates, and frequently changing orientations with respect to the carrying platform or person.
Magnetometers are also found within many mobile devices. In some cases, it has been shown that a navigation solution using accelerometers and magnetometers may be possible if the user is careful enough to keep the device in a specific orientation with respect to their body, such as when held carefully in front of the user after calibrating the magnetometer.
As such, there is a need for a navigation solution capable of accurately utilizing measurements from a device within a platform to determine the navigation state of the device/platform without any constraints on the platform (i.e. in indoor or outdoor environments) or the mobility of the device. The estimation of the position and attitude of the platform has to be independent of the usage of the device (e.g. the way the user is holding or moving the device during navigation).
In the case of portable devices, the device may be tilted to any orientation; it is required that the device provide seamless navigation even in such scenarios.
In addition to the above mentioned application of portable devices, such as for example smart phones and tablets, (that may involve a full navigation solution including position, velocity and attitude, or position and attitude), there are other applications (that may involve estimating a full navigation solution, or an attitude only solution or an attitude and velocity solution) where the method to mitigate the aforementioned problems is needed for enhancing the user experience and usability, and may be applicable in a number of scenarios such as, for example:
Video gaming equipment;
Augmented reality equipment;
Wearable computing devices (such as for example smart wrist watches, and smart glasses); or
APPlication acCESSORIES or Appcessories (such as for example digital wrist watches, electronic glasses, and electronic belt clips).
The main challenge is that the low-cost MEMS sensors in current wearable computing devices, appcessories, or even portable devices are considered insufficient for reliable navigation purposes due to very high noise, large random drift rates, and especially for such mobile devices that can freely change orientation with respect to the platform or person. Some prior solutions to overcome the sensors errors is better error modeling, however this is harder for portable navigation which also still have the hard problem of varying orientation with respect to the platform or person.
Thus methods of further enhancing the performance of navigation solutions (that may involve estimating position, velocity and attitude, or any subset or combination thereof) of portable devices, wearable devices, and/or appcessories among others are needed.